Heisman Trophy-winner and two-time National Football League Pro Bowler Herschel Walker is in possession of a 2-0 mixed martial arts record with two technical knockouts.

Recently-retired ice hockey player Chris Drury won the 1989 Little League World Series before winning silver medals at the Salt Lake City 2002 and Vancouver 2010 Olympic Winter Games and a National Hockey League Stanley Cup Championship with the Colorado Avalanche.

In rugby, Carlin Isles is perhaps the biggest crossover athlete name. Of course, now it comes with the title of "Fastest Man in World Rugby." Isles' track pursuits ended after missing out on the London 2012 Games and the Men's Eagles Sevens have been the better for it: Isles has scored a total of 28 tries in just 14 events on the IRB HSBC Sevens World Series circuit.

Isles followed in the footsteps of Miles Craigwell, who is now in consideration for both Men's Eagles Sevens and Men's Eagles tours after playing American football at Brown University and for a time with the NFL's Miami Dolphins.

Most recently, Green Bay Packers all-time leading rusher Ahman Green stated his interest in pursuing rugby and traveled to the Olympic Training Center in Chula Vista, Calif., for a camp with the Eagles.

"My initial goal was to be on the team," Green said. "I had talked to [former Men's Eagles Sevens Head Coach] Al Caravelli in 2009 and we corresponded through cell phone and email. Then we lost contact. After I lost contact with Caravelli I didn't have any other coaches I could contact so I just kept working out.

"It came later than sooner. A few years passed, [USA Rugby President of Rugby Operations] Nigel [Melville] contacted me and finally got the ball rolling."

"When you actually get out there and have a go it's totally different," Melville said of Green's try-out. "You have to be incredibly fit, you have to run for a long period of time, you have to have great skills. [Ahman's] probably always played attack, but in rugby you're playing defense, as well."

Green's journey to the rugby pitch did not end with the two-day camp at the OTC. In January, he served as the Eagles' team liaison during USA Sevens in Las Vegas, where he was able to witness some of the best sevens teams in the world play the newest Olympic sport.

"I had only seen practice but now, seeing the live game action all day, was a lot," he said. "It actually filled in a lot of gaps for me from a fan standpoint; understanding the game, the tackling, the tries, the concept and the methods to playing good defense and having a good offense."

Green was not the only non-rugby player looking for a chance to get to the Olympics. Some of the newest athletes in Residency at the OTC are crossover athletes.

"The Olympics is always a draw," Melville said. "You hear about sprinters who decide to push a bobsled. Some sports lead to it. In the U.K., they get people off the street just because they're tall and aerobic and they go rowing. It's a very easy crossover sport. Rugby is a more complex crossover sport. It's not quite as easy as people think."

Though he was not given the opportunity to represent the Eagles on the circuit, Green is staying in rugby to help attract some new athletes.

"When I saw the announcement that rugby was going to be in the Olympics, I said, 'That's the closest thing that we as American football players will have to play football [in the Olympics],'" Green said. "I know how we look at football as Americans. We're great at it. We would dominate if they would ever allow football in the Olympics.

"[Rugby] is the next best thing, and the next common sense thing to being allowed. If we have the players, we have the coaches. We kind of have time on our side to get myself and maybe some other athletes that are in my position ready."

Former San Diego Chargers and Buffalo Bills linebacker Shawne Merriman, who retired from the NFL in 2013, said he would "love to participate in the Olympics" playing rugby.

American football players are some of the most in-shape athletes on the planet. Isles was quoted as saying rugby 15s players were "way, way bigger than the guys who play on sevens. I've seen some of those guys on TV and some of them are straight animals - some of them are as big as in the NFL . . ."

At 37 years old (36 at the time of his tryout at the Olympic Training Center), Green is still a model of the NFL regimen.

Merriman, 29, is also staying in shape despite having retired from the gridiron game, and could prove to be an asset for the Men's Eagles Sevens. Though the switch from American football to rugby is not the easiest - nor is it the toughest - Melville thinks an athlete of Merriman's caliber could add to any rugby team.

"It's a new challenge for them and they're great athletes," Melville said of potential NFL crossovers. "There's no doubt about their athleticism, just that they've been built in different ways. They haven't been built like rugby players - they've been built for football."

In 2013, Melville attempted to entice Tim Tebow to make the switch to rugby.

One door closes, an Olympic Rugby door opens for @TimTebow - we should talk about our global game! @USARugby

Following his release from the New England Patriots, Tebow found himself without a job. His representatives declined the offer from USA Rugby, though thousands of fans on social media tried to persuade the former Florida Gator to pick up a rugby ball.

Should he decide to take up rugby, Green thinks a future in the NFL would not be out of the question for the young quarterback.

"We want interest at least," Green said. "Is he interested in keeping his athleticism up for the NFL or is he looking to get a gold medal? If you're on a national rugby team and you end up with the gold, silver or bronze, trust me: an NFL team's going to show some interest. Any NFL coach or scout that knows rugby or understands rugby like I know it, they'll respect that."

Others criticized USA Rugby for targeting an NFL player when thousands of young men playing the game at the collegiate and club level have put in the time to warrant a look at the national team.

While the United States has plenty of talented rugby players of age, those younger players who go on to the NFL, NBA and NHL should also be included in the talent pool.

"The High School sevens team was very good," Green said. "So taking the kids coming up on that scene and guys who are in my age span just ready to go and help out in any way we can, we have a legit chance."

Nate Ebner was a member of the AIG Men's Junior All-Americans at the IRB Junior World Championship in 2008, but quit club rugby at Ohio State to join the Buckeyes' football team. The New England Patriots drafted him in 2012.

"[Ebner] crossed the other way," Melville said. "So football doesn't need our players? They've been trying to get Carlin to go."

"You be honest," Green said of persuading young ruggers to stay with the 80-minute game. "Don't hide anything about it. That's how I learned when I was recruited in high school for football. The recruiter that came to town that was honest with me about what I was getting into? I decided to go to that school. Just shoot straight. That's how you convince a player, because then they're making up their own mind.

"They'll realize what they've already experienced through rugby - the travelling they get to have, first-hand, real life situations. You travel the world. You're in places most people don't get a lifetime to go to. But at 16, 17, 18, you're there meeting people, talking to people, learning how to socialize with people from another country. That in itself is a great experience. It gives the kids an opportunity to grow as a person and a human being."

American football and rugby are closer than some realize, and Green believes both sports could benefit from collaboration.

Hear Ahman Green discuss the opportunity for NFL players to train with rugby players in the offseason:

Former Eagles Sevens included current Eagles 15s players Todd Clever, Takudzwa Ngwenya and Chris Wyles, as well as former players Paul Emerick and Kevin Swiryn. Some of the current crop of Eagles will surely be looking for an opportunity to medal at the Olympic Games, but should NFL players not also have the same chance?

The United States possesses some of the world's greatest athletes. Should a few more start passing the ball backwards, America could very well turn into the next "rugby superpower."